Our objective is to establish a Sexually Transmitted Infection (STI) Cooperative Research Center at the University of Washington (UW) to investigate interactions between the human genital microbiome and syndromes and pathogens that contribute to STI-related morbidity. We will apply our innovative approach of intensive sampling and robust characterization of the genital microbiome to cutting-edge investigation of the underlying biological mechanisms of key interactions between STI pathogens, bacterial communities, and syndromic presentations in two high-risk populations: reproductive-age women and men who have sex with men (MSM). Importantly, our work will go beyond the traditional cataloguing and association studies that have characterized early microbiome research by defining determinants of, and mechanisms underlying, shifts in microbial communities, including interactions of genital bacteria with STI pathogens, triggers of host responses that characterize common syndromes, and local environmental factors; this will in turn inform new approaches to prevention and management. Through robust and experienced Cores, we will provide scientific and leadership infrastructure support for four inter-related Research Projects, Developmental Research Project awards for new investigators, and interactions among CRCs and with NIH. The Research Projects address (1) Determine whether genital HSV-2 shedding increases risk of BV via increased genital inflammation through daily anogenital and vaginal sampling for detection of HSV, Nugent score and BV-associated bacteria (BVAB) to define the temporal relationship between HSV-2 shedding and shifts in the vaginal microbiome in women with HSV-2 and frequent BV. (2) Identify biochemical, microbial and biofilm threshold levels necessary for the development and persistence of BV using an integrated set of clinical, laboratory and modeling studies through self-collected daily vaginal swabs to measure quantitative bacterial and biochemical levels during periods of microbial shifts, including menses, incident BV, and antibiotic treatment, and validation using specialized in vitro systems to measure bacterial growth and competition dynamics under different polymicrobial and biochemical conditions. (3) Define the urethral microbiome in men as it relates to sexual practices, particularly in MSM, and its relationship to urethritis with 16S rRNA gene PCR and sequencing, to identify bacterial communities or species that predict NGU recurrence or persistence after standard antibiotic therapy. (4) Characterize interactions between the vaginal microbiome and hormonal contraceptive delivered in a vaginal ring (CVR), with local immunity and vaginal dysbiosis as primary outcomes, with analysis of the contribution of the CVR to development and maintenance of a protective Lactobacillus-dominant microbiome.